Gas turbine engine with a variable exit area fan nozzle, nacelle assembly of such a engine, and corresponding operating method

ABSTRACT

A turbofan engine includes a fan variable area nozzle having a multiple of vents through a fan nacelle and a sleeve system movable relative to the vents by an actuator system. The fan variable area nozzle changes the effective area of the fan nozzle exit area to permit efficient operation at predefined pressure ratios. The vents include a grid structure which directs and smoothes the airflow therethrough as well as to reduce noise generation.

BACKGROUND OF THE INVENTION

The present invention relates to a gas turbine engine, and moreparticularly to a turbofan engine having a fan variable area nozzlewhich selectively opens vents through a fan nacelle to change a bypassflow path area thereof.

Conventional gas turbine engines generally include a fan section and acore engine with the fan section having a larger diameter than that ofthe core engine. The fan section and the core engine are disposed abouta longitudinal axis and are enclosed within an engine nacelle assembly.

Combustion gases are discharged from the core engine through a coreexhaust nozzle while an annular fan flow, disposed radially outward ofthe primary airflow path, is discharged through an annular fan exhaustnozzle defined between a fan nacelle and a core nacelle. A majority ofthrust is produced by the pressurized fan air discharged through the fanexhaust nozzle, the remaining thrust being provided from the combustiongases discharged through the core exhaust nozzle.

The fan nozzles of conventional gas turbine engines have a fixedgeometry. The fixed geometry fan nozzles are a compromise suitable fortake-off and landing conditions as well as for cruise conditions. Somegas turbine engines have implemented fan variable area nozzles. The fanvariable area nozzle provide a smaller fan exit nozzle diameter duringcruise conditions and a larger fan exit nozzle diameter during take-offand landing conditions. Existing fan variable area nozzles typicallyutilize relatively complex mechanisms that increase overall engineweight to the extent that the increased fuel efficiency therefrom may benegated.

Accordingly, it is desirable to provide an effective, lightweight fanvariable area nozzle for a gas turbine engine.

SUMMARY OF THE INVENTION

A turbofan engine according to the present invention includes a fanvariable area nozzle having a multiple of vents through a fan nacelleand a sleeve movable relative the vents by an actuator system. The ventswhen exposed by movement of the sleeve changes the effective area of thefan nozzle exit area and permits efficient operation at predefinedflight conditions. The fan variable area nozzle is closed to define anominal the fan nozzle exit area and is opened for other flightconditions such as landing and takeoff.

The vents include a grid structure which directs and smoothes theairflow therethrough as well as reduce noise generation by introducingrandomness in the flow stream which breaks the otherwise discretevortical structures to minimize edge tones.

The present invention therefore provides an effective, lightweight fanvariable area nozzle for a gas turbine engine.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the currently preferred embodiment. The drawings thataccompany the detailed description can be briefly described as follows:

FIG. 1 is a general schematic partial fragmentary view of an exemplarygas turbine engine embodiment for use with the present invention;

FIG. 2 is a perspective view of an axially operated FVAN;

FIG. 3A is a perspective side view of a rotationally operated FVAN;

FIG. 3B is a perspective front view of a rotationally operated FVAN;

FIG. 4A is a perspective side view of a radially operated FVAN; and

FIG. 4B is a perspective front view of a radially operated FVAN.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a general partial fragmentary schematic view of a gasturbofan engine 10 suspended from an engine pylon P within an enginenacelle assembly N as is typical of an aircraft designed for subsonicoperation.

The turbofan engine 10 includes a core engine within a core nacelle 12that houses a low spool 14 and high spool 24. The low spool 14 includesa low pressure compressor 16 and low pressure turbine 18. The low spool14 drives a fan section 20 through a gear train 22. The high spool 24includes a high pressure compressor 26 and high pressure turbine 28. Acombustor 30 is arranged between the high pressure compressor 26 andhigh pressure turbine 28. The low and high spools 14, 24 rotate about anengine axis of rotation A.

The engine 10 is preferably a high-bypass geared turbofan aircraftengine. Preferably, the engine 10 bypass ratio is greater than ten (10),the turbofan diameter is significantly larger than that of the lowpressure compressor 16, and the low pressure turbine 18 has a pressureratio that is greater than 5. The gear train 22 is preferably anepicycle gear train such as a planetary gear system or other gear systemwith a gear reduction ratio of greater than 2.5. It should beunderstood, however, that the above parameters are only exemplary of apreferred geared turbofan engine and that the present invention islikewise applicable to other gas turbine engines including direct driveturbofans.

Airflow enters a fan nacelle 34, which at least partially surrounds thecore nacelle 12. The fan section 20 communicates airflow into the corenacelle 12 to power the low pressure compressor 16 and the high pressurecompressor 26. Core airflow compressed by the low pressure compressor 16and the high pressure compressor 26 is mixed with the fuel in thecombustor 30 and expanded over the high pressure turbine 28 and lowpressure turbine 18. The turbines 28, 18 are coupled for rotation with,respective, spools 24, 14 to rotationally drive the compressors 26, 16and through the gear train 22, the fan section 20 in response to theexpansion. A core engine exhaust E exits the core nacelle 12 through acore nozzle 43 defined between the core nacelle 12 and a tail cone 32.

The core nacelle 12 is supported within the fan nacelle 34 by structure36 often generically referred to as an upper and lower bifurcation. Abypass flow path 40 is defined between the core nacelle 12 and the fannacelle 34. The engine 10 generates a high bypass flow arrangement witha bypass ratio in which approximately 80 percent of the airflow enteringthe fan nacelle 34 becomes bypass flow B. The bypass flow B communicatesthrough the generally annular bypass flow path 40 and is discharged fromthe engine 10 through a fan variable area nozzle (FVAN) 42 which definesa nozzle exit area 44 between the fan nacelle 34 and the core nacelle 12at a segment 34S of the fan nacelle 34 downstream of the fan section 20.

Thrust is a function of density, velocity, and area. One or more ofthese parameters can be manipulated to vary the amount and direction ofthrust provided by the bypass flow B. The FVAN 42 preferably includes asleeve system 50 movably mounted to the fan nacelle 34 to effectivelyvary the area of the fan nozzle exit area 44 to selectively adjust thepressure ratio of the bypass flow B in response to a controller C.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 20 of the engine 10 is preferablydesigned for a particular flight condition—typically cruise at 0.8M and35,000 feet. As the fan section 20 are efficiently designed at aparticular fixed stagger angle for an efficient cruise condition, thesleeve system 50 is operated to effectively vary the fan nozzle exitarea 44 to adjust fan bypass air flow such that the angle of attack orincidence on the fan blades is maintained close to the design incidencefor efficient engine operation at other flight conditions, such aslanding and takeoff thus providing optimized engine operation over arange of flight conditions with respect to performance and otheroperational parameters such as noise levels. The sleeve system 50preferably provides an approximately 20% (twenty percent) change in areaof the fan exit nozzle area 44. It should be understood that otherarrangements as well as essentially infinite intermediate positions arelikewise usable with the present invention.

Referring to FIG. 2, the sleeve system 50 generally includes a multipleof vents 52 and a sleeve 54 axially movable along the engine axis Arelative to the vents 52 by an actuator system 56. The sleeve 54 ismounted about the fan nacelle 34 and is movable thereto such as on alongitudinal track system 60 to change the effective area of the fannozzle exit area 44 and permit efficient operation at predefinedpressure ratios. That is, the bypass flow B is effectively altered byopening and closing the additional flow area provided by the vents 52.Seals between the sleeve 54 and the vents 52 prevent leakage. The sleevesystem 50 changes the physical area and geometry of the bypass flow path40 during particular flight conditions. Most preferably, the sleeve isdivided into a multiple of sectors (best seen in FIGS. 3B and 4B) tofacilitate thrust vectoring operations. Preferably, the sleeve system 50is closed to define a nominal converged position for the fan nozzle exitarea 44 during cruise and is opened for other flight conditions such aslanding and takeoff.

The vents 52 are preferably located circumferentially about the fannacelle 34 within the fan end segment 34S downstream of the fan section20. The fan end segment 34S is preferably located adjacent an aft mostend segment of the fan nacelle 34, however, the vents 52 may be locatedin other segments of the fan nacelle 34. The vents 52 preferably includea grid structure 58 which directs and smoothes the airflow therethroughas well as reduces noise generation by introducing randomness in theflow stream to break the otherwise discrete vortical structures andminimize edge tones therefrom.

In operation, the variable area flow system 50 communicates with thecontroller C to adjust the sleeve relative the vents 52 to effectivelyvary the area defined by the fan nozzle exit area 44. Other controlsystems including an engine controller or an aircraft flight controlsystem may also be usable with the present invention. By adjusting theentire periphery of the FVAN 42 in which all segments are movedsimultaneously, engine thrust and fuel economy are maximized during eachflight regime by varying the fan nozzle exit area. By separatelyadjusting the circumferential sectors of the FVAN 42 to provide anasymmetrical fan nozzle exit area 44, engine bypass flow is selectivelyvectored to provide, for example only, trim balance, thrust controlledmaneuvering, enhanced ground operations and short field performance.

Referring to FIG. 3A, another embodiment of the sleeve system 50Agenerally includes a multiple of vents 52A and a sleeve 54A rotatable(FIG. 3B) about the engine axis A such as upon a circumferential tracksystem 60A. The sleeve 54A is mounted about the fan nacelle 34 and ismovable thereto to change the effective area of the fan nozzle exit area44 as generally described above.

Referring to FIG. 4A, another embodiment of the fan variable area system50B generally includes a multiple of vents 52B and a sleeve 54B whichextends and retracts relative the fan nacelle 34 through a linkage 62such as a scissor or trapezoidal linkage or the like to selectivelyexpose and cover the multiple of vents 52B (also illustrated in FIG.4B). It should be understood that various actuation, linkage systems,and sleeve movements will be usable with the present invention.

The foregoing description is exemplary rather than defined by thelimitations within. Many modifications and variations of the presentinvention are possible in light of the above teachings. The preferredembodiments of this invention have been disclosed, however, one ofordinary skill in the art would recognize that certain modificationswould come within the scope of this invention. It is, therefore, to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described. For thatreason the following claims should be studied to determine the truescope and content of this invention.

1. A nacelle assembly for a gas turbine engine comprising: a corenacelle defined about an axis; a fan nacelle mounted at least partiallyaround said core nacelle, said fan nacelle having a multiple of ventsadjacent a fan nacelle end segment, said multiple of vents incommunication with a fan bypass flow; and a sleeve movable relative tosaid multiple of vents to vary an effective fan nozzle exit area.
 2. Theassembly as recited in claim 1, wherein said sleeve is radially movablerelative to said axis relative to said vents.
 3. The assembly as recitedin claim 1, wherein said sleeve is axially movable relative to saidvents.
 4. The assembly as recited in claim 1, wherein each of saidmultiple of vents includes a grid therein.
 5. A gas turbine enginecomprising: a core engine defined about an axis; a gear system driven bysaid core engine; a fan section driven by said gear system about saidaxis; a core nacelle defined at least partially about said core engine;a fan nacelle mounted at least partially around said core nacelle, saidfan nacelle having a multiple of vents adjacent a fan nacelle endsegment, said multiple of vents in communication with a fan bypass flow;and a sleeve movable relative to the multiple of vents to vary a fannozzle exit area.
 6. The engine as recited in claim 5, furthercomprising an actuator system to radially move said sleeve relative tosaid fan nacelle.
 7. The engine as recited in claim 6, furthercomprising a controller in communication with said actuator system tovary said fan nozzle exit area in response to a flight condition.
 8. Amethod of varying an effective fan nozzle exit area of a gas turbineengine comprising the steps of: (A) selectively moving a sleeve relativea multiple of vents adjacent a fan nacelle end segment, the multiplevents in communication with a bypass flow to vary a fan nozzle exit areain response to a flight condition.
 9. A method as recited in claim 8,wherein said step (A) further comprises: (a) at least partially openingthe vents to communicate a portion of the bypass flow therethrough toincrease the effective fan nozzle exit area in response to a non-cruiseflight condition.
 10. A method as recited in claim 9, wherein said step(a) further comprises: (i) axially sliding the sleeve relative themultiple of vents.
 11. A method as recited in claim 9, wherein said step(a) further comprises: (i) rotating the sleeve relative the multiple ofvents.
 12. A method as recited in claim 9, wherein said step (a) furthercomprises: (i) moving the sleeve relative the multiple of vents.
 13. Theassembly as recited in claim 1, wherein said sleeve is rotationallymovable about said axis relative to said vents.
 14. The assembly asrecited in claim 1, wherein said sleeve is formed from a multiple ofsections, each of said sections movable relative to a multiple of vents.15. The assembly as recited in claim 1, wherein said sleeve is movableadjacent an outer surface of said fan nacelle between a first positionand a second position, said first position forward of said multiple ofvents.
 16. The assembly as recited in claim 1, wherein said sleeve islocated about an outer surface of said fan nacelle.